Pestoh



A. HOLMES. PISTON.

APPLICATION FILED AUGJG. I917. 1,3 1 1, 1 24'. latvnted July 22, 1919.

2 SHEETSSHEET D.

HTTORNEY.

I A. HOLMES.

PISTON.

APPLICATION FILED AUG-16.!917.

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2 g i/VVENTOR Wm/ fiTToR/vcYs' Anrnun HOLMES, orcanron, omo.

Heron.

Specification of Letters Patent. Patented J 11y 22, 1919.

Application filed August 16, 1917. Serial No. 186,510;

This invention relates to certain improvements in pistons and is particularly adapted for use in internal combustion engines of automobiles, motor-boats and the like and this application is filed as a continuation in art of my former copending application, erial No. 133,918, filed November 28, 1916 for pistons.

In the use of gas engines, the eificiency of the engine depends to a, considerable extent upon the rapid cooling of the piston and the'cylinder, and the difficulty has been to transfer or conduct the heat particularly from the central portion of the piston, (the hottest part of practically all gm engines) rapidly enough to permit high efficiency of the engine.

The cylinders of such engines have usually been made of cast ironand, to a considerable extent, the pistons have been formed 'of the same material or at least a material of substantially the same coefiicient of expansion as the material of which the cylinder is formed, so that the clearance (perhaps 3 or 4 one thousandths of an inch) between the piston and the cylinder will remain practically uniform at all temperatures, preventing rattling and clapping of the piston and causing it at all times to move in substantially accurate axial relation with the cylinder.

However, cast iron and other suitable material of like coeilicient of expansion is not capable of conducting the heat from the central portion of the piston to the wall of the cylinder with suficien-t rapidity to permit high efficiency operation of the engine.

To avoid this difiiculty, pistons have recently been formed of material having a high heat conductivity, such as aluminum. The difiiculty with pistons of this character lies in the fact that aluminum has with high drawings, is a full, clear, and

heat conductivity also a high coefficient of expansion, substantially double that of cast iron. The use, therefore, of aluminum or material having a different coeflicient of expansion from that of the cylinder, in the formation of pistons results in either of two conditions. e

F irst.'The piston must be of materially less diameter than the cylinder when cold permitting considerable clearance and resulting in what is generally called piston slaps or,

Second. If the clearance is small, the piston and cylinder will seize when hot.

Thus the cast iron piston has a distinct advantage in that its coefficient of expansion is the same as that of the cast iron cylinder for any given change of temperature, while the aluminum piston is much more effective in producing high engine efliciency, due to its assistance in rapidly cooling the cylinder and the engineas a result ofits high heat conductivity.

The object, therefore, of this invention is to produce a. piston having all the advantages of the high conductivity of an aluminum piston combined with the advantages .of a piston formed of a material having the same or approximately the same coeflicicnt of expansion as the cylinder in which it Works. This object is accomplished by forming the top portion of the piston exposed to the high temperature of the combustion chamber, of aluminum or similar material of high heat conductivity and giving this portion of the piston a sufficient clearance so it will not seize the cylinder when hot, while the lower portion, of sufficient length to constitute a bearing, to cause the piston at all times, whether hot or cold,

to move axially of the cylinder without slapan operable, eflicient piston of this type, due

to the method herein shown and described of connecting the two parts at their axes only and allowing symmetrical, uniform expansion radially from the connecting means throughout the entire area of the parts without in any way altering the substantially accurate, circular form of the parts.

In the drawings- Figure 1 is a top plan view of the piston.

Fig. 2 is an elevation ofthe same.

Fig. 3 is a section on line 3-3, Fig. 2.

Fig. 4 .is a bottom plan view of the upper section of the piston.

Fig. 5 is a top plan view of the lower sec tion of the piston.

Fig. 6 is a vertical sectional view through a. piston of my invention illustrating the difierent diameters of the section in an exaggerated manner, and showing a portion of a cylinder within which the piston is adapted to move. a

As stated, the piston shown in the drawings is adapted for assembly with the usual cylinder 11 'of an internal combustion engine, such cylin-derbeing usually formed of cast iron, other similar material being perhaps utilizable- The piston 1, as shown, is formed in two sections, an upper section -.2 of aluminum or other suitable material of high heat conductivity, and incidental to such high conductivity having a coefficient of expansion considerably greater than that of the cast iron cylinder a within which it is adapted to work, and a lower section -.3- formed of cast iron or other suitable material having a coeflicient of expansion the same as that .of the cylinder within which the piston works and, therefore, of a coeflicient of expansion considerably less than that of the aluminum upper section.

Preferably the assembled piston tapers slightly from its lower end toward its upper en and the aluminum upper section 2 is of slightly less diameter than the lower section -3.

It will be apparent that the two parts may be of any desired relativelength so long as the lower section 3 is of suflicient axial length to constitute a bearing for the piston, causing the same to move axially of the cylinder without slapping or rattling, and in the specific illustration shown, the lower section 3---v is formed of .cast iron and embodies the radial wrist-pin bosses 4 and 5 near ,or approximately at its upper end, and preferably a reinforcing ange 6 adjacent its lower end.

' This section 3 is provided with a cross wall 7, of which the upper portion of the bosses -.4- and may constitute Par lie-in me ia po n e ween s bosses preferably being arched, as shown, at

nausea -8 and formed with a boss 9- having a. central opening disposed axially of the i ylinder and internally threaded for a purpose hereinafter described.

The upper section 2 may preferably, as shown, be of inverted cup-shape and having a central, axially-projecting boss 10 formed with a central threaded opening terminating in a frusto-conicalseat 11 in which the head 12 of a screw -13 is adapted to be countersunk, the screw passing through and having a threaded engagement with the alined interiorly threaded openings in the bosses -9-- and -10'--, and preferably the lower end of the screw may be spun over into engagement with the adjacent arched portion 8 of the cross wall 7-' to constitute a permanent rigid connection between the two parts of the piston.

When the bosse 9 and 10- are in firm contact, the circumferential wall 14:- of the section 2- rests tightly upon the upper edge of the lower section 3 to constitute a substantial continuation thereof, its radial movement resultant from expension under varying degrees of temperature relatively to the section -3- being free and unobstructed.

In the form shown, the upper section -2 is provided with the usual eircumfer ential grooves -15 for the reception of. piston rings, and the upper portion of the bosses 4- and 5 or the transverse wall -7 may be provided with perforations or openings -16 permitting the passage f lubricant to the wrist-pin bearings.

The section -2 is provided with a series of reinforcing ribs 17 tapering outwardly from the bpss 10 and merging into the outer wall of the section to strengthen the wall of the piston directly exposed to the force of combustion within the cylinder (not shown).

It will be apparent that the only connecting means between the two sections of the piston is the boit 13 arranged substantially axially of said sections and that the outer edges or circular wallsof the sections have planular surfaces normal to the axis of the piston, which surfaces are free to move or slide radially relatively to each other under the action of varying temperatures to which the different sections are subjected, and in accordance with their varied coefiicients of expansion.

As illustrative of one relative proportionate size of parts, the following may be referred to: Y With a cast iron cylinder of 3%" or 4 internal diameter, the section 3 of the P W may ave a clearance of 3 or 4 one l dths of an inch, while the aluminum section '2 at the greatest diameter may have a clearance of from 6 to 8 one-thouexterior adapted to closely fit the interior of the engine cylinder.

With thecconstruction here shown, the sec tion --3- at low temperatures constitutes the bearing for the entire piston, while un der highdegrees ofvheat, the entire piston said sections having concentric axial has a substantially continuous cylindrical exterior closely fitting the interior 0]": the

, engine cylinder throughout the entire length of the piston.

. AlthoughI have shown and described one specific form, arrangement and size of sections and one specific means for attaching the'same to permit free expansion of both parts, radially of the connecting means, I do not desire to limit myself to the same as various changes may be made in the details of form, construction, size, arrangement, and means of attachment without departing from the spirit of this invention as set forth in the appended claims.

Vhat I claim is l. A piston comprising a substantially cylindrical section having a coefiicient of expansion substantially equal to that of the cylinder within which the composite piston is adapted to move, an inverted cu shaped section of relatively high heat 00nd ctivity,

and peripheral abutting surfaces lying in a plane substantially normal to the axis of the composite piston and means connecting the axial abutting portions permitting free radial expansion of the sections independently of each other.

2. A piston comprising a substantially cylindrical section having a coeiiicient of expansion substantially equal to that of the cylinder within which the composite piston is adapted to move, section of relatively sald sections having an inverted-cup shaped high heat conductivity, concentric axial and peripheral abutting surfaces lying in a plane substantially normal to the axis of the com posite piston and a bolt extending through and connecting the axial abutting portions of said sections, permitting free radial expansion of the sections independently of each other, the axis of the composite piston lying in said bolt.

3. A piston comprising two sections of difierent heat conductivity and of difi'erent diameters connected at their axes only, and free to expand radially independently of each other.

4. A piston comprising a'substantially cylindrical section having a coeflicient of expansion substantially equal to that of the cylinder within which the composite piston is adapted to move, an inverted cup-shaped section of relativelyhigh heat conductivity and of less diameter than said cylindrical section, said sections having concentric axial and peripheral abutting surfaces lying in a plane substantially normal to the axis of the composite piston, and means connecting the axial abutting portions, permitting free radial expansion of the sections independently of each other.

5. A piston comprising an inverted cupshaped upper section of high heat conductivity and a substantially cylindrical lower section having a smaller coeflicient of expansion and being of greater diameter than the cup-shaped section, and means connecting the two sections permitting free radial expansion and contraction of each independently of the other.

6. A piston comprising an upper section formed of material of high heat conductivity, a lower substantially cylindrical sec tion of greater diameter than the upper section and having a cross wall at its upper end, one of said sections provided with an axial boss extending-into contact with the other section, and means positioned substantially axially of the composite piston and extending through said boss and connecting the upper section to said cross wall.

7. In combination with a cylinder, a piston movable in the cylinder and comprising a cup-shaped upwardly tapered head-por tion formed of material of high heat-conductivity and a substantially cylindrical base portion formed of material having a coefiicient of expansion substantially the same as the coeflicient of expansion of the material of which the cylinder is formed, and means securing said portions together permitting free radial expansion of the body of the cup-shaped head independently of said base portion.

8. In combination with a cylinder, a piston comprising a head-portion formed of material of high heat-conductivity and a substantially cylindrical base-portion formed of material having a coefficient of expan sion substantially the same as the coefiicient of expansion of the material of which the cylinder is formed, said portions being of different external diameter and formed of material of diii'erent cocliicient of expansion, and means securing said portions together permitting free radial expansion of the head-portion independently of said base-portion.

9. In combination with a cylinder, apiston comprising a head-portion formed of material of high heat-conductivity and a. substantially cylindrical base-portion formed my ei-mm of material having a coefficient of expam contraction of each inclepenclently of the 10 sion substantially the same as the coefficient other. of expansion of the'material of which the in witness whereof I have 'hereunto set cylinder is formed, said portions being of myh'and this 8th day of August,'1917.

' diflerent external diameter and formed'of ARTHUR HOLMES material of difierent coefficient of expan sion, and means connecting the two portions Witnesses:

at substantially the axis of the composite GRACE BUCHTEL, piston permitting free radial expansion and E 0. THOMPSON. 

